Shaft furnace

ABSTRACT

In a shaft furnace for burning granular material, three vertically extending similarly constructed shafts are arranged with their axes forming the corners of an equiangular triangle, each shaft has an annular channel and each annular channel is interconnected to the annular channels in the other two shafts by separate crossover canals. The crossover canals are connected to each annular channel at angularly spaced positions. Further, the crossover canals extend between the annular channels at the location where the shafts are closest together.

United States Patent 1191 Tschinkel Jul 9, 1974 [54] SHAFT FURNACE 1,325,674 l2/l9l9 Hutchins 432/95 [75] Inventor: Friedrich Tschinkel, Thalwil,

Switzerland Primary Examiner.lohn J. Camby Assigneezv Maen ofenbaulAG Zurich Attorney, Agent, or F1rm-Toren, McGeady and Switzerland Stangar [22] Filed: Apr. 18, 1973 21 Appl. No.: 352,221 [57] ABSTRACT 1 In a shaft furnace for burning granular material, three 30 Foreign Application priority Data vertically extending similarly constructed shafts are t arranged with their axes forming the corners of an Apr. 24, I972 Austna 3 583/72 q ng triangle, each Shaft has an annular chan [52] U 8 CI 432/95 432/l28 432/207 nel and each annular channel is interconnected to the [51] a 2 annular channels in the other two shafts by separate [58] i 130 133 crossover canals. The crossover canals are connected 1 5 to each annular channel at angularly spaced positions.

Further, the crossover canals extend between the an- [56] References Cited nular channels at the location where the shafts are UNITED STATES PATENTS c1086 mgether' 393,672 11/1888 Solvay 432/95 4 Claims, 5 Drawing Figures PATH-NED L 74 SHEET 1 BF '3 SHAFI FURNACE SUMMARY OF THE INVENTION The present invention directed to a shaft furnace and, more particularly, the individual shafts forming the furnace are interconnected by separate nonintersecting crossover canals.

In the present invention a shaft furnace is provided for burning granular material and the furnace consists of three circular or polygonal shafts of the same construction with their axes arranged at the corners of an equiangular triangle, that is with the sides of the triangles spaced sixty degrees apart. In operation, one of the shafts is heated as the granular material and combustiongases flow concurrently downwardly and the combustion gases exit from the lower end of the combustion zone of the heated shaft and pass into the other two shafts and flow upwardly in counter flow relationship to the downwardly moving material. During each cycle of operation each of the shafts is heated for a given period while the other two shafts receive the combustion gases from the heated shaft. Each of the shafts has a combustion zone located intermediate its upper and lower ends with a preheating zone above the combustion zone and a cooling zone below the combustion zone. Each shaft has an annular channel located in the region between the combustion zone and the cooling zone and the annular channels in each shaft are located at the same level. Separate crossover canals extend from each of the annular channels to the annular channels in the other two shafts.

ln British Patent 4,166/1902, a furnace plant is disclosed composed of four shafts and four channels systems. In this furnace plant, the first channel system supplies the heating gas to one of the shafts while the second channel system is used for conveying hot air from the shaft being cooled to the shaft in which combustion takes place. In the third channel system the combustion gases are conveyed from the shaft in which thecombustion takes place to a preheating shaft and the fourth channel system is used to discharge the combustion gases into achimney. During each phase of operation, one of the shafts is cut out and the other three shafts are connected in series. As a result, a complicated conduit system is required for interconnecting the shafts and the connections are alternatively arranged at the lower and upper portions of the shafts.

Further, shaft furnaces are known for heat treating granular material, for example, for burning limestone and such shaft furnaces consist of three interconnected shafts. In this arrangement, one of the shafts is heated with the heating gases flowing concurrently with the downwardly moving material to be treated while the combustion gases flow from the lower end of the heated shaft and pass in countercurrent flow with the material in the other two shafts. After passing downwardly through the heated shaft, the combustion gases exit from the material into an annular channel about the shaft in the region between the combustion zone and the cooling zone and from the annular channel the combustion gases flow through crossover canals into lar channels and the crossover canals are located at the same level. With the crossover canals in the form of a three-armed star there is the advantage that the condition of the combustion gases can be easily tested at the intersecting point of the canals, however, this advantage is negated by the following significant disadvantages.

a. The combustion gases from the annular channel in the heated shaft flow from two directions into its associated crossover canal. As a result, where the two flows of the gases meet in the annular channel at the entrance to the crossover canal they are deflected in a right angle direction. Both of these flow phenomena, the meeting of the two flows of gases and their deflection, causes very vigorous turbulence which continues in the crossover canal and results in significant dust deposits.

Depending on the alkali content of the dust and the S0 content of the combustion gases, the deposited dust may form solid crusts which have a very significant negative effect on the flow of the gases through the crossover canals. Accordingly, the deposited dust must be periodically removed. Another cause of turbulence in the crossover canals is the separation of the flow from the crossover canal of the heated shaft into the two crossover canals of the other shafts. The turbulence which develops'at the point of intersection of the three crossover canals has the further disadvantage that, when the fuel is not completely burned within the heated shaft, the formation of turbulence causes an intimate and complete mixing of unburnt substances with the combustion air and cooling air and after-burning takes place which results in locally higher wall temperatures and causes a strong sintering of the dust deposits.

b. The cross-section of the crossover canals is limited, it is not permitted to fall below a predetermined flow velocity, because the ceiling of the canals should, for static reasons, be situated on the same level as the ceiling of the annular channels and their base or floor should be located higher than the base of the floor of the annular channels which is determined by the pile of material within the shaft, to prevent the deposit of burnable material on the base of the crossover canals.

c. The length of the crossover canals and, accordingly, the length of the floor on which the dust can become encrusted, cannot be shortened below a minimum length. The reason for this is that the locations at which the annular channels of two adjacent shafts are closest to one another, the walls separating them must be of a dimension of at least 2 X 250mm (two normal brick lengths).

d. The ceiling or roof over the crossover canals must be made in the form of a flat or straight arch. Suspended roofs cannot be used for the crossover canals because, on one hand, it is difficult to seal such roofs to the shafts at the annular channels (such a furnace operates at excess pressure) and, on the other hand, such a suspended construction would make it very difficult to provide openings in the roof for poking, agitating or taking measurements. As a result, it is necessary to form the roof of the crossover canals from three flat or straight arches in a cross formation. With such a roof construction, its length is greater in the center and decreases toward the abutments. Such an arrangement is undesirable from a load point of view. As the width of the crossover canals is increased, then the shorter is the roof at the abutments or supports. Further, there is a limit to the width of the crossover canals.

It is the primary object of the invention to afford a shaft furnace which overcomes the disadvantages experienced in the known shaft furnaces. The problems previously faced are overcome by interconnecting the annular channel of each shaft to the annular channels of the other two shafts by separate crossover canals which extend along the sides of the triangle defined by the axes of the shafts. In this arrangement, the flow of the combustion gases from the heated shaft are directed into two separate crossover canals so that each canal carries only about half of the gas as compared to the previously known arrangements. Moreover, the crossover canals are located at the positions where the annular channels of the shafts are closest to one another and the wall construction required in the star-like arrangement of the crossover canals of the prior art can be partially avoided and the shafts can be positioned closer to one another and, as a result, the crossover canals can be made shorter in length.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. I is a horizontal sectional view of a prior art shaft furnace having three shafts interconnected at the level of the annular channels about the shafts;

FIG. 2 is a view of the roof formed over the crossover canals;

FIG. 3 is a vertical sectional view of two shafts of a three shaft furnace which embodies the present invention;

FIG. 4 is a horizontal sectional view taken along the line lVlV of FIG. 3; and

FIG. 5 is a view of the roof formed over the crossover canals of the shaft furnace shown in FIG. 3 and FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION In the drawing, FIGS. 1 and 2 disclose a prior art arrangement of a shaft furnace having three shafts disposed in a triangular arrangement while FIGS. 3, 4 and 5 are directed to a shaft furnace embodying the present invention.

In FIGS. 1 and 2 the shaft furnace consists of three shafts I, 2, 3 each having alaterally arranged annular channel 4, 5 and 6. The annular channels 4, 5 and 6 are interconnected by crossover canals 7, 8 and 9 which intersect at a common point located between the three shafts so that the axes of the three canals provide the appearance of a three-armed star.

The form of the roof covering the crossover canals is shown in FIG. 2. It would be preferable if the openings, shown in dashed lines, could be provided on the axes of the crossover canals, however, if the dashed line openings were used it would weaken the arch construction. Accordingly, usually a single opening is provided in the roof at the intersection of the three crossover canals to afford access to the canals for cleaning or measurement purposes.

In FIGS. 3 and 4 a shaft furnace similar to the one shown in FIGS. 1 and 2, is illustrated, however, a different arrangement of the crossover canals is provided.

As shown in FIG. 4, the shaft furnace is made up of three vertically extending shafts 1, 2, 3 with the shafts arranged in a triangular arrangement. That is, the axes of the three shafts are located at the corners of a triangular pattern and the lines connecting the axes form the sides of the triangle. In FIG. 3 the shafts 1, 2 are shown filled with the material to be burned and the shaft 3 is similarly filled with the material. Each shaft is divided into a combustion zone B located intermediate its upper and lower ends with a preheating zone A extending upwardly from the upper end of the combustion zone and a cooling zone C extending downwardly from the lower end of the combustion zone. The upper part of the preheating zone A with the charging device is not shown in FIG. 3 nor is the lower end of the cooling zone illustrated with the discharge arrangement.

In FIG. 3, two fuel supply conduits 11, shown in dotdash lines of a plurality of supply conduits (not shown), are located within the shaft 1 which, for purposes of this explanation, is assumed to be the heated shaft. The combustion air supplied to the combustion zone is indicated by the arrow 10 at the upper end of the shaft while the arrows 12 at the transition from the combustion zone to the cooling zone indicate the flow of the combustion gases out of the shaft into the annular channel 4 which laterally surrounds the shaft at the lower end of the combustion zone B and the upper end of the cooling zone C. The combustion gases within the heated shaft 1 flow concurrently downwardly with the material being treated. The combustion air is supplied into the shaft at a point above the level of the material,

that stabe preheatins .ZQQEA tt e r d wnward passage through the combustion zone B, the combustion gases exit from the heated shaft 1 through the pile 15 of material at the upper end of the cooling zone C. The pile 15 of material is formed by the enlargement of the cross-section of the shaft which commences at the lower end of the combustion zone. The brickwork 13 of the shaft is supported by pillars l4 and the support arch has a polygonal form.

A shaft 1 is connected through its annular channel 4 with the annular channel 5 in shaft 2 through crossover canal l6 and it is connected with the annular channel 6 in shaft 3 through the crossover canal 17. Further, in addition to the crossover canal 16 between shafts 2 and l, shaft 2 is connected to shaft 3 by crossover canal 18. Accordingly, each of the shafts has two separate crossover canals extending from its annular channel for interconnection with the other two shafts. As distinguished from the arrangement illustrated in FIG. I, the crossover canals l6, l7 and 18 in FIG. 4 are separate from one another and do not intersect. As a result, the combustion gases exiting from the heated shaft pass through two separate crossover canals into the other shafts.

By providing two separate crossover canals from each annular channel, a doubling of the cross-sectional area of the canals is achieved as compared to the single crossover canal arrangement from each shaft is disclosed in the prior art, note FIG. 1. Further, the width of each crossover canal in FIG. 4 is not limited in the same manner as the star-shaped interconnected arrangement of FIG. I. With the flat or straight arch which forms the roof over each crossover canal, it is possible to provide a simple roof arrangement whose width span is always larger toward the supports or abutments and is shorter at the center portion between the shafts which provides a particularly advantageous arrangement with regard to the stability and life of the structure, note FIG. 5. Moreover, the openings 19 into the crossover canal, used for poking, agitating or measuring, can be positioned in ideal locations without negatively affecting or disturbing the stability of the roof over the crossover canals. In contrast, if the openings shown in dashed lines in FIG. 2 were used it would limit the stability of the roof where the crossover canals interconnect at a point intermediate the shafts. Accordingly, in the prior art it was not possible to locate the openings into the crossover canals at the locations which would be most favorable from an operational point of view.

- The essential advantage of the triangular arrangement of the crossover canals l6, l7 and 18 shown in FIG. 4, resides in substantially improved flow conditions. Considering the shaft 1 as the heated shaft the combustion gases exit from the lower end of the combustion zone through the pile 15 of the, material being treated into the annular channel 4 and separate into two oppositely directed gas flows, one passing to the crossover canal l6 and the other flowing in the opposite direction to the crossover canal 17. Accordingly, the two separate flows do not contact one another at the discharge points from the annular channel and, thus, avoid causing turbulence. Further, the flow of gas through each of the crossover canals flows directly into a single other shaft and the deflection at the fork of the arrangement in FIG. 1 is avoided. Therefore, the formation of turbulence within the crossover canals is considerably less than occurred under the prior art arrangement. With the arrangement of the crossover canals shown in FIG. 4 dust deposits within the canals are significantly reduced. Moreover, no baffle or impact surfaces are located in the path of the gases. Due to the larger cross-sectional areas of the canals the speed of flow is significantly reduced. Due to the reduction in turbulence and the decrease in speed, the material transfer coefficient is reduced and this transfer coefficientis determinative of the separation of the alkali content and the transfer of S to the dust deposits. Experiments have indicated that with a low material transfer coefficient, the deposits of dust consist, in the main, of CaO. Such deposits do not form crusts and are not very strong, as a result, if they reach a certain thickness the deposits fall apart on their own. Moreover, due to the reduction in turbulence, any afterbuming occurs only when the combustion gases enter into the material in the exit shafts, a phenomenon which is completely harmless. In the triangular non-intersecting arrangement of the crossover canals of the present invention, the maximum speeds within the annular channels 4, 5 and 6 are also substantially reduced. In the intersecting arrangement of the crossover canals shown in FIG. I, the annular channel of the heated shaft accommodates all of the combustion gases flowing around 360 of the channel. However, in the triangular arrangement of the crossover canals, the exiting combustion gases passing into the annular channel require only a flow in one direction or the other along 180 of the shaft to reach one of the crossover canals, note the flow indicated by the arrows in FIG. 4. Accordingly, the maximum combustion gas velocity in the annular channel of the FIG. 4 arrangement is only about half of the maximum speed in the arrangement shown in FIG. 1. The other half of the combustion gases flow directly from the material in the heated shaft into the material contained in the other two shafts.

Each cycle of operation of the shaft furnace consists of three periods of about 10 to 15 minutes each. During each period a different one of the three shafts acts as the heated shaft while the other two shafts receive the discharge flow from the heated shaft. Therefore, during each cycle each shaft is heated for one period and acts as a discharge member for the other two periods. In each of the three shafts, cooling air is blown in from the bottom as indicated by the arrows 20 in FIG. 3. The cooling air is not used for combustion purposes but serves exclusively for cooling the burnt material.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

. What is claimed is:

1. A shaft furnace, such as for burning granular materials, includes wall means forming three vertically extending laterally spaced shafts of similar construction, the vertical axes of said shafts are arranged in a triangular pattern with the axis of each shaft located at a different corner of the triangular pattern and the sides of the triangular pattern defining angles of approximately each said shaft forming a vertically extending space therein divided transversely of the vertical axis into a vertically combustion section intermediate its upper and lower ends, a vertically extending preheating section located above said combustion section and a vertically extending cooling section located below said combustion section, said wall means forming a horizontally extending annular channel for each said shaft with said annular channel disposed laterally outwardly of and encircling its respective said shaft and said wall means arranged to provide an opening between said shaft and said annular channel which surrounds it, said annular channels being located at the junction of said combustion and cooling sections within said shafts, said annular channels encircling said shafts all being arranged at the same level, and said wall means forming a plurality of crossover canals interconnecting said annular channels, wherein the improvement comprises that each said crossover canal extends between and interconnects two of said annular channels and each said annular channel has two said crossover canals connected to it at angularly spaced apart positions and each one of the two said crossover channels is connected to a different one of the other said annular channels so that each said annular channel is connected to each of the other said annular channels.

2. A shaft furnace, as set forth in claim I, wherein the axes of said crossover canals are located along the sides of the triangular pattern defined by lines connected the axes of the three said shafts.

3. A shaft furnace, as set forth in claim I, wherein each said crossover canal extends between two of said annular channels along a line representing the shortest distance between said annular channels.

4. A shaft furnace, as set forth in claim 1, wherein said crossover canals each have an arch roof with openings formed in said arch roofs for poking and agitating material within said crossover canals and for taking measurements within said crossover canals, said openings being spaced from the axis of the passage through said crossover canals connecting two of said annular channels. 

1. A shaft furnace, such as for burning granular materials, includes wall means forming three vertically extending laterally spaced shafts of similar construction, the vertical axes of said shafts are arranged in a triangular pattern with the axis of each shaft located at a different corner of the triangular pattern and the sides of the triangular pattern defining angles of approximately 60*, each said shaft forming a vertically extendinG space therein divided transversely of the vertical axis into a vertically combustion section intermediate its upper and lower ends, a vertically extending preheating section located above said combustion section and a vertically extending cooling section located below said combustion section, said wall means forming a horizontally extending annular channel for each said shaft with said annular channel disposed laterally outwardly of and encircling its respective said shaft and said wall means arranged to provide an opening between said shaft and said annular channel which surrounds it, said annular channels being located at the junction of said combustion and cooling sections within said shafts, said annular channels encircling said shafts all being arranged at the same level, and said wall means forming a plurality of crossover canals interconnecting said annular channels, wherein the improvement comprises that each said crossover canal extends between and interconnects two of said annular channels and each said annular channel has two said crossover canals connected to it at angularly spaced apart positions and each one of the two said crossover channels is connected to a different one of the other said annular channels so that each said annular channel is connected to each of the other said annular channels.
 2. A shaft furnace, as set forth in claim 1, wherein the axes of said crossover canals are located along the sides of the triangular pattern defined by lines connected the axes of the three said shafts.
 3. A shaft furnace, as set forth in claim 1, wherein each said crossover canal extends between two of said annular channels along a line representing the shortest distance between said annular channels.
 4. A shaft furnace, as set forth in claim 1, wherein said crossover canals each have an arch roof with openings formed in said arch roofs for poking and agitating material within said crossover canals and for taking measurements within said crossover canals, said openings being spaced from the axis of the passage through said crossover canals connecting two of said annular channels. 